(1) Field of the Invention
This invention relates to an electromotive gear-shift control apparatus for bicycles, and more particularly to an apparatus which uses human pedaling force as the power for gear shifting, and on the other hand uses an electric motor to determine a control displacement for the gear shifting.
(2) Description of the Prior Art
A conventional gear-shifting system of a bicycle is usually an apparatus with only mechanical components. Such an apparatus can generate a displacement signal (i.e., a displacement force) usually by means of a manual control bar on the bicycle handle, which the displacement signal will cause a plurality of co-axial sprockets on the hub to shift in a predetermined order. However, the control of a complete mechanical gear-shifting system is dominated by the human force applied to the control bar, and unfortunately the difficulty in applying a sufficient control force always exist, especially in severe operating surroundings; for example, while in riding a bicycle uphill or in a rush speeding for a race. Apparently, under these conditions, it is difficult to shift a gear with ease. In case of failure to shift a gear in any situations similar to aforesaid, the bicycle might stop immediately as a result of losing driving force, or the rider has to re-operate the control bar. Occasionally, it is quite possible that any mistake during those emergency maneuvering could endanger the rider.
Recently, the emergence of the electromotive gear-shift system for bicycles is specially aimed at improving the drawbacks of the complete mechanical gear-shift system. The electromotive gear-shift system may generally includes three types as follows:
First type (such as disclosed in U.S. Pat. No. 4,946,425 and U.S. Pat. No. 5,328,414) comprises a DC motor, a reducing gear train, and a gear-switch mechanism. The operation of this type is usually to transmit a driving force out of a DC motor to the gear-switch mechanism through the reducing gear train, and then the gear-switch mechanism will complete the gear shifting. The output parts of this type of gear-shifting system are a guide chain and a sprocket, and the function thereof is similar to the conventional transmission apparatus; i.e., the gear shift to be done by means of a sprocket and a chain.
Second type (such as disclosed in U.K. Patent BG 2,295,868) comprises a DC motor, a reducing gear train, and a gear-switch mechanism for controlling a steel cable of a transmission apparatus. The function achieved by this type is similar to that by the manual transmission bar, except for the DC motor driving a reducing gear train for directly controlling the displacement of the cable to complete the gear shift operation.
The aforesaid first and second types of electromotive gear-shift systems are both utilizing a unique motor to provide the necessary driving force for a gear shift. Therefore, the power consumption in gear shifting is high, and thus a high-capacity power supply is required for the gear shift operation. Since it is impossible to carry an additional battery set on a bicycle, the only way to gain sufficient electricity supply is to strengthen and improve the power-generating capability in the bicycle. Apparently, such a measure would definitely cause the rider to bear more operation loading in generating required electricity.
Third type of the electromotive gear-shift system as shown in FIG. 1 includes a transmission apparatus 430, which is controlled by a transmission control apparatus 500. The gear-shifting driving force of the transmission control is supplied with the pedal driving force 420, which is converted by means of the mechanical displacement control 503 of the transmission control apparatus 500. The gear-shifting difference of the transmission apparatus can be done by means of the transmission selector 400 to be operated by the rider (the transmission selection selector 400 is usually a push-button to replace the conventional control-bar (or shifting lever) as the gear-shifting switch) to input a transmission instruction into the controller 410. Then, the motor 501 regulated by the controller 410 is used for performing the gear-shifting according to the control signal from the controller 410 so as to control the displacement (i.e., the output) of the mechanical displacement control 503. By means of the state monitor 505, the state of the mechanical displacement control 503 is fed back to the controller 410.
The U.S. Pat. No. 5,358,451 is deemed as the third type of electro-motive gear-shift system. The aforesaid gear-shift system, mounted to the rear hub and the chain sprocket, includes two electromagnetic valves or a DC motor, and a transmission mechanism for having the transmission system coupled with the electromotive gear-switch mechanism as a driving force upon gear shifting. The two electromagnetic valves or the DC motor is used for connecting the transmission mechanism and the gear-switch mechanism so as to control the gear engaging or gear disengaging. The characteristics of the switch mechanism in the third type are similar to that in the first type; i.e., by using a sprocket to guide a chain for performing gear shifting.
The third type of electro-motive gear-shift system in the art has no similar drawbacks as mentioned in the aforesaid first and second types, but the mechanism of such system is more complicate, and only suitable for the rear transmission system. Therefore, the application and the cost of the third type is deemed to be not economical.
Consequently, the inventor of the present invention has developed an improvement of the electro-motive gear-shift control apparatus in accordance with the third type of electro-motive gear-shift system so as to obtain a new apparatus having simple structure and broader applicability.